Food preservation and processing methods and related products

Question 1

Name the 3 main processes in the conversion of muscle to meat

Answer 1

• Acidification
• Rigor mortis
• Conditioning

Question 2

Describe acidification in the presence of oxygen

Answer 2

Glycogen breaks down to pyruvic acid and then to CO2 i H2O (with synthesis of ATP)

Question 3

Describe acidification in the absence of oxygen (postmortem)

Answer 3

Glycogen breaks down to lactic acid – no blood to remove LA – acidification (from pH 7.2 to pH 5.5)

Question 4

Describe acidification of meat

Answer 4

• pH drops in beef muscle 36-48 hours, pig 4-8 hours
• Protein denaturation, meat paler and more opaque - its ability to bind water decreases
• pH drop is critical for meat qualities

Question 5

What is the ultimate pH for normal meat?

Answer 5

5.6-6.2

Question 6

Describe PSE acidification and its characteristics

Answer 6

Pale soft exudative

• accelerated anaerobic glycolysis: fast and excessive drop in pH to 5.2-5.4
• Characteristics: poor water holding capacity, pale colour, soft texture, cooking losses (lower processing yield), poor colour in cured products

Question 7

Describe DFD acidification and its characteristics

Answer 7

Dark firm dry

• Not enough glycogen (6.0-6.2 or up to 6.8)
• Characteristics: dark, dry surface (high water holding capacity), shorter shelf life and poor consumer perception of quality

Question 8

What is the onset of rigor mortis solely controlled by?

Answer 8

The availability, or not, of ATP

Question 9

Describe how rigor mortis occurs

Answer 9

ATP can no longer be generated by glycolysis and is eventually exhausted, the muscles lose this relaxed state and pass into rigor

Question 10

How is rigor mortis different in stressed animals?

Answer 10

Stressed animals: less glycogen and ATP = more rapid rigor

Question 11

Why is rigor important for meat quality?

Answer 11

Rigor is important because it fixes the lengths of the sarcomeres, and therefore the muscle’s length and the potential texture of the meat:

• Muscles entering rigor in a very contracted state tend to produce tough meat
• Those entering rigor in a relaxed, or stretched, state will produce tender meat

Question 12

Muscles should enter rigor mortis at what temperature for optimum tenderness

Answer 12

10-15°C

Question 13

What is the effects of fast chilling of carcasses after slaughter?

Answer 13

Cold shortening - the resulting meat is tough

Question 14

What is the main objective of electrical stimulation?

Answer 14

Accelerate the pH decline after death in order to be able to implement a chilling system without any risk of cold contraction

• An electrical current is passed through a carcass to ensure that the meat is tender under rapid carcass chilling.
• It accelerates the normal PM changes (depletion of glycogen and ATP) so that muscle sets in rigor mortis sooner and carcasses can be chilled without fear of cold-shortening and toughening.

Question 15

Describe the process of conditioning

Answer 15

• Natural process which improves eating quality of beef: flavour and tenderness
• Conversion of muscle to meat: natural enzymes from muscle degrade specific proteins from muscle fibers
• Enzymatic proteolytic degradation results in an increase of meat tenderness

Question 16

What are the different recommended ageing times before meat is consumed?

Answer 16

• Poultry 1 day
• Pork 4-10 days,
• Lamb 7-14 days,
• Beef 10-21 days

Question 17

What is meat chilling critical for?

Answer 17

Meat hygiene, safety, product shelf-life, appearance and eating quality

Question 18

When should carcass chilling start, at what temp?

Answer 18

Within 1hr of exsanguination and occur so that a temp of 4°C or less is reached within 24hrs

Question 19

What are the 3 mechanisms of dry chilling?

Answer 19

• Slow air refrigeration
• Rapid air refrigeration
• Ultra-Rapid air refrigeration

Question 20

Describe Slow air refrigeration

Answer 20

Used rarely, in small abattoirs with traditional technologies, three steps:
• carcass ‘draining’ or ‘drying’ at ambient temperature for a few hours,
• pre-refrigeration (around 10°C; 75% relative air humidity) and
• refrigeration (4–7°C, 85–90% relative air humidity).

Question 21

Describe rapid air refrigeration

Answer 21

Most common, carcasses are exposed to air at 1 to -1°C, 90% relative air humidity and 1–3 m/sec circulation for 24–36 h (cattle) or 18–24 h (pigs, lambs); weight loss is around 1.5–2.0%.

Question 22

Describe the 2 phases of ultra rapid air refrigeration

Answer 22

• Carcasses exposed to intensive circulation (2–4 m/sec) of very cold (-4 to -6°C, even -20°C) and humid (90–100%) air in special tunnels for 1–3 h
• Then, refrigeration at -1 to 2°C for 18–22 h (cattle) or for 14–16 h (pigs) with slow air circulation (0.1 – 0.3 m/s). Weight loss only 1%.
• Problem – “cold shortening”

Question 23

Which two problems are associated with wet chilling

Answer 23

Cross contamination and water absorption

Question 24

What is the problem associated with spray chilling

Answer 24

Surface stays wet, better survival of microorganisms

Question 25

Which meat has the longest and shortest shelf life

Answer 25

``` Longest = Beef carcasses – 3-4 weeks Shortest = Offal – 3 days ```

Question 26

What are the main signs of meat spoilage?

Answer 26

Meat greening (with or without fluorescence) and slime layer

Question 27

What is the purpose of aerobic packaging?

Answer 27

Prevents secondary contamination, but doesn’t extend shelf life

Question 28

Bacteria and yeasts in meat are inhibited at what temperature when freezinf?

Answer 28

Bacteria inhibited at –7°C, yeasts at –12°C

Question 29

How does slow vs rapid freezing affect bacteria

Answer 29

Slow freezing - better survival of bacteria | Rapid freezing – water inside bacterial cell crystallises leading to cell death

Question 30

Name some other food preservation and processing methods

Answer 30

- cooking - salting and curing - smoking and drying - fermentation - thermal treatments

Question 31

Describe the methods of drying meat

Answer 31

Removal of the water - Most often carried out by keeping the product suspended in air - Lyophilization (“Freeze drying”) - the meat is first frozen and then exposed to a very low pressure of around 5–6mbar (‘in vacuum’) at -20°C to -40°C, then removing the ice by sublimation

Question 32

Based on their final aw values, dried foods can be divided into which three groups?

Answer 32

- High moisture products - Intermediate-moisture products - Low-moisture products

Question 33

Describe smoking as a food preservation treatment

Answer 33

- A result of aerobic or anaerobic pyrolysis of woods - It starts at around 170°C, and at temperatures up to 270°C is endothermic, and above that has an intensive exothermic nature - Cold (30oC), warm (40-60oC) or hot (70-80oC) smoking - Can be hardwood smoke or liquid (injected) - It should not be higher than 300°C

Question 34

Define fermentation

Answer 34

Phase of intensive growth and metabolism of lactic acid bacteria accompanied with rapid fall of pH or: Any partial breakdown of carbohydrates taking place in the absence of oxygen

Question 35

Which factors affect the microbial growth in food?

Answer 35

* Intrinsic – associated with the food itself * Extrinsic – related to the environment where the food is placed e.g. temp, humidity * Factors related to the microorganisms themselves

Question 36

Name some food additives

Answer 36

* Polyphosphates - increase the ability of meat proteins to bind water. Enable incorporation of additional water * Antioxidants (Ascorbic acid) * Food colours * Preservatives * Sweeteners * Flavour enhancers * Emulsifiers

Question 37

Which foodborne pathogen is most sensitive to dry chilling?

Answer 37

Campylobacter jejuni

Question 38

What is the water activity (Aw) of food?

Answer 38

Proportions of available water in food for microorganisms needs

Question 39

How does adding salt affect microbial growth and survival in food?

Answer 39

Reduced water activity in food

Question 40

Microorganisms that can grow in dry food are called?

Answer 40

Xerophilic

Question 41

How are pasteurised products stored?

Answer 41

Refrigeration